The declining California population of Western Purple Martins: why & how can we assist its recovery?

The declining California population of Western Purple Martins: what are the causes of decline and how can we assist its recovery?
Dan Airola, Conservation Research and Planning
The Western Purple Martin (Progne subis arboricola) has declined dramatically in California following the arrival of the European Starling in the 1970s. Understanding of the species current status is hampered by the species’ sparse and widely distributed remnant populations and lack of funding and interest by wildlife agencies and conservation organizations. In 2009, I led the only recent large-scale survey of sites known to be occupied in the 1980s and 1990s. We showed a decline in occupancy through much of the species’ range, except in the densely forested northern coast region. The Sacramento bridge-nesting martins are the last population in the 18,000 square-mile Central Valley. This urban population avoided starling competition by adopting urban overpasses as nesting sites. Sacramento supported the largest martin concentration in California through the early 2000s, when 172 pairs were counted. The population then declined rapidly for reasons that were mysterious, until by 2021 only 23 pairs (12% of the former population) remained. Extensive evaluation has implicated the rapid rise in the use of neonicotinoid insecticides since the 2000s as the likely cause of the species’ decline. Sacramento martins also continue to be plagued by disturbance caused by construction of infrastructure, transportation, and urban development projects. My recent (2021) book comprehensively summarized research finding and appropriate strategies for project planning, design, environmental analysis, and construction to protect this unique population until pesticide issues can be addressed. These recommendations have been adopted by some agencies. Purple Martin recovery in California will require a better understanding of causes of decline, more protection for colonies, reduction in insecticide use, and initiation of new management techniques including nest boxes, which so far have only been adopted at two sites in the state.